A Working Group, under the auspices of the Council on Epidemiology, American Heart Association, is engaged in pooling the data from eight longitudinal, epidemiological studies of coronary heart disease, in order to obtain predictive estimates or risk toward the development of this disease which no single study could obtain, on account of the shortage of numbers which results when available data are subjected to analysis within detailed sub-categories. These sub-categories relate to the various manifestations of coronary heart disease (myocardial infarction with and without survival, sudden death, cardiovascular deaths not preceded by overt myocardial infarction, angina pectoris with and without survival) and their associations, singly and combined, with single and multiple combinations of risk factors (serum cholesterol, systolic and diastolic blood pressure, smoking and relative weight). The latter risk factors will also be related to cerebrovascular and peripheral vascular disease, total deaths and non-cardiovascular deaths. Substudies (e.g. analyses of the significance of resting and exercise electrocardiograms; the intercorrelations between risk factors) will be included. Results will be expressed in terms of incidence rates, life tables and multiple logistic function analyses. These data will make it possible to assess the risk of the various clinical manifestations of atherosclerosis in hitherto unprecedented detail, with a view to preventing clinical disease in susceptible individuals. Eight studies are presently enrolled (Framingham, Albany, Los Angeles, Minneapolis (two), Chicago (two), and Tecumseh.